The present invention relates to an electronic control method and system for internal combustion engines and more particularly to a control method and system well suited to smoothly effect the engine control under all operating conditions.
In the past, an engine control system of the type employing a CPU (central processing unit) as an electronic engine control unit to control an engine has been disclosed, for example, in "Systems and Controls", vol 24, No. 5, p.p. 306-312, 1980.
In this case, a method of determining the actual fuel injection quantity Q.sub.f by adding various corrections to a basic fuel injection quantity determined on the basis of an intake air flow rate Q.sub.a and an engine speed N is used. In this system, the respective correction factor are determined on the basis of the actual car tests and they are determined to take the form of values incorporating the results of feeling evaluations.
The air-fuel ratio (A/F).sub.A of the exhaust gas is measured by an O.sub.2 sensor so as to determined whether the calculated fuel injection quantity Q.sub.f has resulted in the optimum combustion. This determination is effected unifiedly under all operating conditions and the value of Q.sub.f is feedback controlled in accordance with the deviation of the measured air-fuel ratio (A/F).sub.A from the desired air-fuel ratio (A/F).sub.R.
The operation program for executing the above-mentioned processing is started in accordance with a time interval and a degree of engine crankshaft rotation. This means that the control is effected by noting only the average movements of the air and fuel drawn into the engine and the exhaust gas.
The above-mentioned prior art techniques have given no consideration to the setting up of a target reference, the updating of calculation models for fuel injection quantity and ignition timing, the measurement of the flow of clusters of gases having bearing on the combustion, etc., and thus they are disadvantageous in terms of economy (fuel consumption) driveability and riding comfort.
Moreover, the conventional control methods have noted the average movements of an engine thus failing to accurately grasp the combustion in each cylinder and thereby making it impossible to properly control the combustion in each cylinder separately.